Aluminum base alloys



Patented F eb. 17, 1942 UNITED STATES PATENT OFFICE No Drawing. Application April 16, 1937, Serial No. 137,280. Renewed August 4,-19-39.

Great Britain May 5, 1936 2 Claims.

This invention comprises improvements in aluminum base alloys and in particular aluminum alloys comprising copper with nickel, magnesium, iron and silicon.

In the production of cast pieces of aluminum base alloys, by which may be understood alloys containing more than 70% of aluminum, it is desirable to secure the finest possible size of grain. The grain referred to is the macrostructure, which is recognizable by the naked eye on smooth surfaces or sections of the cast pieces after they have been etched in suitable reagents, such as an aqueous solution of caustic soda, or hydrofluoric acid.

In castings a diminution in grain size improves the mechanical properties. The finer the'grain size characteristic of an aluminum alloy, other things being equal, the better its founding properties in that the tendency to cracking in the mold is reduced and the production of sound castings is facilitated. In cast pieces intended to be forged, pressed, extruded or otherwise worked mechanically, a fine grain size is desirable because it assists the attainment of good mechanical properties in the subsequent working.

The object of the invention is to produce aluminum alloys having a fine grain, and possessing in consequence of this fine grain superior mechanical properties in the cast condition and also when forged and also after heat-treatment of the castings and forgings according to known processes.

'According to this invention, a relatively small proportion of columbium, also known sometimes as niobium, as added to an aluminum alloy, particularly an alloy of copper, nickel, magnesium, silicon, and iron, the alloy thereby acquiring a fine grain, which is maintained over a wide range of conditions of melting, casting and working. We have found it convenient to make the proportion of columbium 0.1% to 0.2% of the total weight of the alloy. We have observed appreciable grain refinement with as little as0.05% of columbium, and on the other hand we have not found it generally necessary or desirable to exceed 0.5% Qfcolumbium.

We have discovered that these beneficial effects are exhibited in the alloy mentioned above containing the elements set out below in .the proportions stated:

Per cent -Copper 0.5 to 12 Nickel 0.5 to Magnesium 0.1 to 3 Silicon 0.2 to 2.5 Iron 0.2 to 2 Columbium 0.05 to 1- The beneficial efiect of the columbium is not dependent upon the manner in which it is incorporated in the alloy, but a convenient procedure is to add it in the from-of ahardenerf or mother alloy or prealloy relatively rich in columbium. According to one practical process, the first stage in the incorporation of the columbium in the aluminum alloy is the preparation of an aluminum alloy relatively rich in colum-' .bium from ferro-columbium and aluminum. The

ferro-columbium may be in the form of an alloy containing approximately equalparts of iron and columbium with impurities such 'as tantalum, silicon and carbon in small proportions. In preparing the columbium hardener alloy, aluminum is melted in a crucible and its temperature raised to 1100 to 1200 C. A weight of ferrocolumbium equal to approximately one-tenth of the weight of aluminum is stirred into the molten aluminum, or is carried in a perforatd container which is moved up and down in the aluminum, until the addition is entirely dissolved. In this way an alloy containing approximately 5% columbium, 5% iron, with the balance substantially aluminum, is obtained. This is cast into molds, remelted in a crucible, allowed to solidify and remelted without unnecessary superheating, in

order to eliminate gases which may have become absorbed through they heating to high temperatures in the initial operation. After this presolidification treatment, the alloy is cast into suitable ingot molds.

One practical process for making up an alloy using the aluminum "hardener alloy relatively rich in columbium may be described. The final alloy to be made according to this example has the following nominal composition:

Per cent Copper 2.5 Nickel 1.5 Magnesium 0.8 Silicon 1.2 Iron l.2 Columbium 0.1 Aluminum Remainder The hardener alloys employed are: aluminumnickel with 20% nickel, aluminum-iron-columbium with 5% iron and 5% columbium, aluminum-iron with 10% iron, aluminum-copper with copper, aluminum-silicon with 20% silicon.

Aluminum is melted in a crucible and the calculated quantities of hardeners are stirred in successively in the order in which they are The alloy described is suitable for the manufacture of castings and forgings, and responds effectively to the known processes or heat-treatment applicable to aluminum alloys containing copper, nickel, magnesium, silicon and iron. For example, a large improvement in mechanical properties of forging's of the alloy is obtained by a two-stage heat-treatment in which the parts are first heated for 4 hours at 530 0., then quenched in water, reheated for 16 hours at 165 C. and finally quenched in water again.

A valuable feature of the grain refining action of columbium is that it is effective even when the aluminum alloy is raised to a high temperature before casting. As an illustration of the efficacy of the grain refining action of columbium. it may be mentioned that, when an alloy 0! the composition stated above is cast at 800 G. into a dried sand mold to form a cylindrical block 3" high and 3" diameter, the grains visible in the macrostructure after etching have diameters of 0.2 to 1 mm., whereas the same alloy not con taining columbium, cast under the same condi- Per cent Copper 2.5 Nickel 1.5 Magnesium 0.8 Silicon 1.2 Iron 1.2 Columbium 0.1 Aluminum Remainder 2. Aluminum base alloy containing 0.5% to 12% copper, 0.5% to 5% nickel, 0.2% to 2.5% silicon, 0.1% to 3% magnesium, 0.2% to 2% iron, 0.05% to 1% columbium, remainder aluminum; the columhium acting to produce in the alloy 3.

' fine grained structure which is maintained over a wide range of melting, casting, and working conditions, and to raise the ratio of the ductility of the alloy to its tensile strength without decreasing the tensile strength.

ALFRED JOHN MURPHY. STANLEY ALFRED EDWARD WELLS. 

